1) Field of the Invention
The present invention relates to a wholly aromatic copolyamide and a shaped article thereof. More particularly, the present invention relates to a wholly aromatic copolyamide and a shaped article thereof, especially a fiber, having excellent mechanical properties, for example, tensile strength, ultimate elongation and tensile modulus, high resistances to heat and chemicals, a satisfactory solubility in organic solvents, and a good processability and workability.
2) Description of the Related Arts
It is known that conventional wholly aromatic polyamides (aramids) have an excellent high tensile strength and modulus and a high heat-resistance, and thus are useful for forming various shaped articles, for example, fibers and films. Especially, a para-type aramid resin, i.e., poly-p-phenylene terephthalamide (PPTA) is useful, as a typical aramid resin, for industrial materials and protective materials in which the above-mentioned properties are effectively utilized.
Nevertheless, industrial materials must have not only a high tensile strength but also a high ultimate elongation, and thus the conventional para-type aramid resins are not always satisfactory as industrial materials.
Many attempts have been made to overcome the disadvantages of the conventional para-type aramid resins. For example, Japanese Unexamined Patent Publication No. 62-263,320 discloses fibers comprising a blend of an aromatic copolyamide prepared by copolymerization of p-phenylene diamine, terephthalic acid, and an aromatic diamine or dicarboxylic acid monomer having a naphthalene ring structure, with poly-p-phenylene naphthalamide.
Also, Japanese Unexamined Patent Publication No. 63-75,111 discloses aromatic polyamide fibers comprising a copoly-(p-phenylene terephthalamide/2,6-naphthalamide) containing copolymerized 2,6-naphthaldiamine in an amount of 5 to 10 molar %.
The inventions disclosed in the above-mentioned Japanese publications effectively eliminate the disadvantage, i.e., a low ultimate elongation, of the conventional shaped PPTA articles, for example, fibers, but difficulties arise in the production and shaping processes of the PPTA resin and copolymerized or modified PPTA resins, due to a high rigidity of the polymeric molecules thereof. For example, in the preparation of a uniform solution of the PPTA or copolymerized or modified PPTA resin as a polymerization reaction medium for the resin, hexamethylphosphortriamide, which is harmful to the human body and other living bodies, or an organic polar solvent mixture containing a metal salt, for example, calcium dichloride or lithium chloride, must be used in a large amount of 9% by weight or more, as disclosed in Japanese Unexamined Patent Publication No. 62-263,320. Alternatively, a specific organic polar solvent containing 4% by weight or more of a metal salt, for example, calcium dichloride, as mentioned in Japanese Unexamined Patent Publication No. 63-75,111, must be used as a polymerization reaction medium. Even if this type of copolymerization reaction medium effectively dissolves the polymer, the resultant polymer solution is gelled, and thus the copolymerization process must be carried out by utilizing a specific technique for handling a gelled material having substantially no mobility or fluidity. Further, in the shaping process, for example, a spinning or film-forming process, the gelled polymer solution cannot be used as a shaping dope solution. Namely, the polymer must be dissolved in concentrated sulfuric acid to provide a liquid crystalline dope solution for the shaping or spinning, i.e., a liquid crystal-shaping or spinning process must be carried out. When this process is utilized, a large amount of a neutralizing agent must be employed to neutralize the sulfuric acid in the dope solution, and this neutralizing procedure unavoidably causes the resultant product to be undesirably contaminated with inorganic ions derived from the neutralizing agent, and thus the quality of the product is lowered. Also, the use of the concentrated sulfuric acid causes the operational environment to be dangerously polluted and the shaping apparatus to be corroded, and thus is disadvantageous from the viewpoint of industrial convenience.
To eliminate the above-mentioned disadvantages due to the polymerization medium, several attempts have been made to utilize a popular organic polar solvent to provide an isotropic shaping (spinning) dope solution, and to make the shaping (spinning) procedure simple and easy. Particularly, the solubility of the polyamide resin is enhanced by introducing ether bonds (--O--) into the molecular chains of the polyamide, as disclosed, for example, in Japanese Unexamined Patent Publication Nos. 51-76,386, 51-134,743, 51-136,916, 61-252,229, 62-27,431, 62-225,530, 62-177,022 and 62-177,023 and Japanese Examined Patent Publication No. 53-32,838.
In those prior references, the wholly aromatic copolyamide consisting of a copolymerization product of p-phenylene diamine (PPDA) and 3,4'-diamino phenylether 3,4'-DAPE) with an aromatic dicarboxylic acid component has an excellent mechanical strength, rigidity and chemical resistance, and is capable of being dissolved by N-methyl-2-pyrrolidone, which is a popular organic polar solvent and useful as a polymerization reaction medium. Also, the resultant copolyamide solution obtained from the copolymerization reaction in the polymerization medium, can be directly utilized as a doping solution for various shaping (spinning) processes.
The introduction of the ether bond into the polymeric molecular chain effectively causes the resultant polymeric molecular chains to become flexible and the resultant copolymer to exhibit the above-mentioned advantages, but the resultant copolymer article is disadvantageous in that it has an unsatisfactory mechanical strength and elongation property.
Under these circumstances, a wholly aromatic polyamide having not only a high mechanical strength, satisfactory elongation property, and good heat resistance, but also a high solubility in popular organic solvents and able to be produced by a polymerization process such that the resultant polymer solution therefrom can be directly utilized as a dope solution for various shaping (spinning) process, has not been realized.
Japanese Examined Patent Publication No. 53-32,838 discloses wholly aromatic copolyamides which are copolymerization products of a dicarboxylic acid component consisting of terephthalic acid and 2,6-naphthalene dicarboxylic acid with a diamine component consisting of p-phenylenediamine and 3,4'-diaminodiphenylether. The wholly aromatic copolyamides disclosed in the Japanese publication are preferably limited to those having a content of copolymerized 2,6-naphthalene dicarboxylic acid component of 20 to 80 molar % based on the total molar amount of the dicarboxylic component and a component of copolymerized 3,4'-diaminodiphenylether of 15 to 80 molar % based on the total molar amount of the diamine component.
Also, Japanese Unexamined Patent Publication No. 61-195,123 and 62-27,431 discloses reaction catalysts and additives for the polymerization of aromatic dicarboxylic acids with aromatic diamines. The aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalene dicarboxylic acid. The aromatic diamines include p-phenylene diamine and 3,4'-diaminodiphenylether.
Nevertheless, those three Japanese Publications failed to disclose specific aromatic copolyamides which are soluble in a popular organic polar solvent and can be produced by a copolymerization process in the solvent such that the resultant copolyamide solution can be directly utilized as a dope solution for a shaping or spinning process, and which can be converted to a shaped article having an excellent mechanical strength and ultimate elongation not obtainable by the conventional copolyamide articles.